The present invention is directed to a clamping system in which a plurality of workpiece holding clamps are mounted upon a clamping frame which is in turn mounted upon a conveyor to convey a workpiece clamped on the frame to a series of successive work stations at which various operations are performed upon the workpiece. The invention is especially concerned with the handling of relatively large panel type workpieces, such as the major body and door panels which are to be subsequently assembled into an automotive vehicle body.
The initial step in the construction of an automotive vehicle body is the stamping of various panels, such as body side panels, the floor panel, and the door panels from sheet metal. Before these various stamped panels are assembled into the vehicle body, additional components such as panel reinforcements, mounting brackets, etc., are welded in place on the panel and other components, such as door hinges or, in the case of door panels, door latch and window operating mechanisms, are assembled onto the panel by conveying the panel to each of a series of successive work stations at which various work operations are performed upon the panel. For production efficiency, it is desired that the panel be initially located at an accurately predetermined position at each work station by the conveying or transfer system. The size and irregular shape of the typical panel is such that in order to fixedly support the panel in a predetermined position, the panel must be engaged by clamps at several different locations on the panel and the clamps in turn must be mounted at fixed locations upon a rigid clamping frame carried by the conveyor or transfer device.
All such systems must include some arrangement for actuating the clamps at a loading station where the panel is initially loaded and clamped to the clamping frame and a second clamp actuating arrangement at the final station on the production line where the completed panel is unclamped and unloaded from its clamping frame. Optimum production efficiency is achieved where all of the various work operations to be performed on the panel can be performed while the panel remains clamped to its clamping frame. However, it is not always possible to design the clamping frame and to locate the panel engaging clamps in a manner such that access to all regions of the panels upon which work operations are to be performed is possible. In these cases, it is necessary to unclamp and transfer the panel from its clamping frame to a fixture permanently located at the work station for performance of the work operation and to then reload and reclamp the panel upon its clamping frame for transfer to the next work station. Rapid loading or unloading of the panel from or to the frame requires that several clamps, typically irregularly spaced around the periphery of a relatively large irregularly shaped panel, be substantially simultaneously actuated to clamp or to unclamp the panel, and this objective may be best achieved by actuating the clamps from a common power source. However, the clamps are mounted upon a clamping frame which must be conveyed along a production line of substantial length with the individual clamps maintained in their clamping position at least while the frame is moving along the production line. Clamps of the type employed typically are actuated by a relatively short stroke pneumatic motor mounted directly upon the clamp, and the maintaining of a connection between an air pressure source and a plurality of individual pneumatic motors moving along a production line of substantial length presents some obvious problems.
The present invention is directed to a clamp actuating system by means of which a plurality of clamps mounted upon a clamping frame movable along a conveyor line may be simultaneously or substantially simultaneously power actuated to their clamping position or to their release position and be positively maintained in the position to which they were last actuated without requiring continued application of power to the clamp actuator.